October 22, 1996

Article at The American Reporter

Earth-Crossing Asteroid Search Faces Extinction

How asteroids are found: the single point of reflected light against the background of stars moving as the Earth turns

by Wilson da Silva
American Reporter Correspondent 

CANBERRA, Australia – The world’s first truly global effort to detect and track the thousands of asteroids with the potential to strike the Earth is about to crash just as it was getting off the ground. 

Run by three Australian astronomers, the asteroid watch program for the Southern skies is essential to the international project. But the program, the only Southern Hemisphere tracking of asteroids, will come to a halt at the end of the year when Australian government funding runs out – despite the fact that Australian cities have a better than one in 100 chance of being annihilated by an impact within the next century. 

Astronomer Duncan Steel, who grudgingly runs the modest Australian asteroid discovery and tracking program, told the Australian and New Zealand Association for the Advancement of Science (ANZAAS) congress last month that the global average chance of any individual dying due to an asteroid impact is one in 5,000. This is based on an asteroid at least 1.6 miles in diameter striking the Earth, an event that is estimated to occur once every 100,000 years. This compares with a one in 20,000 chance of someone dying in a plane crash in the United States, or the global average of one in 75,000. 

But a much smaller object slamming into the biggest target on Earth – the Pacific Ocean – could devastate Pacific Rim countries. “You only need a 100 to 200 meter (yard) object, even if it blew up in the atmosphere over the Pacific, to generate a blastwave would cause a tsunami 100 meters (yards) high with a range of 1,000 kilometers (620 miles),” he said. 

“It would spread out and wipe out every single city in the Pacific Rim. Now, the chances of that occurring in the next century are better than one in 100,” he said. 

A 200-foot asteroid did strike the atmosphere in 1908, exploding between 10 and 13 miles above Siberia. Trees in the Tunguska area were ignited by the heat of the explosion and immediately flattened by the ensuing blastwave. In total, more than 850 square miles were completely devastated, an area almost the size of Luxembourg. 

“That sort of event occurs, we believe, once a century somewhere around the Earth,” Steel told the congress. 

The Australian program, based at the Siding Spring Observatory’s Schmidt wide-aperture telescope, located in mountainous terrain 320 miles north-west of Sydney, involves three nights per month of observation. The astronomers take two pictures of an area of the sky, separated by a few minutes, and then compare the frames. Asteroids, which move in tangent to the sky, appear in the exposures as a “streak” when the plates are put together. 

Once an asteroid is detected, the Australians notify the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who in turn notify asteroid tracking programs in the northern hemisphere. Other astronomers then track the new asteroid during their night-time, helping to obtain a more accurate picture of the object’s orbit. When an asteroid is discovered by observatories in the north, the Australians are similarly notified, and help track it during their night-time, sharing the information with their colleagues. 

The Australians have discovered 10 percent of all Earth-crossing asteroids since the program began in 1990, and are responsible for one-third of all astrometric, or asteroid tracking, data produced. 

There are an estimated 2,000 to 3,000 asteroids that cross the Earth’s orbit. Astronomers know this because, when scanning the skies for new asteroids, for every 20 new ones spotted only one (or five percent) turn out to be previously known asteroids. “Because of that we know that we’ve still got 95 per cent of them to find, and that leads to our value of between two and three thousand,” said Steel. 

An asteroid tracking program has been run by the University of Arizona in tandem with the Australians for a number of years, while a multi-million dollar joint project between the U.S. Air Force and NASA’s Jet Propulsion Laboratory has only just started up in Haleakala, the extinct volcano on the Hawaiian island of Maui.

Ironically, the Australian funding – involving $80,000 a year (with another $80,000 coming from the U.S. Air Force) – is being withdrawn just as the first detailed global search is being mounted. 

“By dint of it’s location, and the fact it is the most technologically-developed Southern Hemisphere nation, Australia has a special responsibility thrust upon it,” Louis Friedman, executive director of the U.S.-based Planetary Society, recently appealed in the letters page of The Australian, a national newspaper. The search program “has been vital to the worldwide effort,” he wrote. 

Steel said he would prefer not to be running the Southern Hemisphere program at all – he believes it is the responsibility of the Australian defense department. Either way, the worldwide effort is now in danger of falling apart because of Canberra’s short-sightedness, he said. 

“Excepting perhaps a global nuclear war, the only catastrophe with the capability to end civilization is an impact by a sizable asteroid,” Steel said. “If, having realized the danger is there, we do not take steps to ascertain whether an impact is due within the next century, this could prove to be the greatest act of folly ever perpetrated by humankind.”